FIG. 1 depicts a diagram of telecommunications system 100 in the prior art. Telecommunications system 100 comprises wireless telecommunications terminals 101-1 through 101-L, wherein L is a positive integer that is equal to five in the example depicted; access point 103 that serves basic service area 110; and telecommunications network 120, all of which are interconnected as shown.
Basic service area 110 is the service area in which shared access to other nodes in telecommunications system 100 is provided to telecommunications terminals such as terminals 101-1 through 101-L. As depicted in FIG. 1, basic service area 110 is in an IEEE 802.11 wireless local area network. In area 110, the one or more wireless telecommunications terminals that make up the basic service set of area 110 are able to access other nodes in system 100 via a shared-communications channel supported by access point 103.
Telecommunications network 120 is a telecommunications network such as the Internet, the Public Switched Telephone Network (PSTN), and so forth. Network 120 comprises or is connected to one or more transmission-related nodes such as gateways, routers, or switches that are used to direct packets from one or more sources to the correct destinations of those packets.
The service provided by the path that links a first node with a second node is characterized by its “quality of service.” Quality of service, for the purposes of this specification, is defined as, from one node to another, a function of the (i) bandwidth, which can be expressed in units such as bits per second, (ii) error rate, which can be expressed in units such as bit errors per number of bits transmitted, and (iii) latency, which can be expressed in units such as seconds. For example, a shared-communications channel that links a wireless terminal such as terminal 101-1 with an access point such as access point 103 is subject to a quality-of-service level.
Each of telecommunications terminals 101-1, for l=1 through L, is a communications device such as a local area network telephone, a notebook computer, a personal digital assistant (PDA), a tablet PC, and so forth. Terminals 101-1 through 101-L are assigned fixed Internet Protocol addresses and, as wireless stations, are assigned Internet Protocol addresses from a pre-specified block of addresses. Terminals 101-1 through 101-L communicate, through access point 103, with other telecommunications terminals that have connectivity with network 120. In order to communicate, a user at a first telecommunications terminal in system 100, such as terminal 101-1, places a “call” (e.g., voice call, email, text chat, video, etc.) to a user at a second terminal in system 100.
Each telecommunications terminal may use a “codec,” as is known in the art, to more efficiently transmit user information, such as voice signals, by compressing the transmitted information and decompressing the received information. A codec has an associated “codec rate” that specifies how much (compressed) information actually has to be transmitted per unit time.
System 100 has to be able to determine whether to admit each call. Call admission control is necessary, considering that terminal 101-1 is also competing with other terminals in its basic service area (i.e., area 110) for the shared-communications channel provided by access point 103. In fact, access point 103 has to be able to handle multiple traffic streams—each stream comprising a series of packets—that are transmitted to or from wireless terminals via the corresponding shared-communications channel.
Furthermore, each terminal has an associated level of mobility. A terminal that is immobile (i.e., is fixed) is able to support a maximum data rate that is more-or-less constant. In contrast, as a mobility-capable terminal moves closer to or away from its access point, the maximum data rate at which the terminal is able to communicate with the access point changes during a call. When the terminal is close to the access point, the signal is generally stronger and, as a result, the maximum data rate is higher. Likewise, when the terminal is far from the access point, the signal is generally weaker and, as a result, the maximum data rate is lower. As a result, the actual shared-communications channel bandwidth that the terminal utilizes—that is, the channel occupancy used by the terminal—during a call changes over time. Furthermore, there can be multiple terminals using the shared-communications channel for calls, where each terminal is able to move independently of one another during a call.
In some techniques in the prior art, the spatial distribution of the different terminals within the basic service area might be considered during the call admission process. This is advantageous in that it considers the data rates for the actual shared-communications channel, instead of merely using data rates from an analytical model of the basic service area. However, this is disadvantageous in that the terminals, being at different distances from the access point, have different supported data rates, which can cause the call admission criterion to have greater variance and lower the utilized bandwidth. As a consequence in some cases, the net effect is to allow fewer calls.